All safety designs have dual-channel safety conditions. The existence of these safety conditions determines the state of the safety output. If the dual-channel safety conditions are fully satisfied, the safety output contacts are closed, and if the safety conditions are abnormal in one way, the safety output contacts are disconnected.
The safety relay monitors the dual-channel input signal in real time. If the safety conditions change, the safety output contact of the safety relay will be disconnected instantly.
Whether it is manual start or automatic start, the safety relay will feedback and monitor the functional integrity of the safety output control object.
The function of the control object is normal, the safety relay is activated, and the control object has a function abnormality in the last cycle (the contact of the AC contactor is stuck), the safety relay cannot be activated this time, and the safety relay will not be restarted until the abnormality is eliminated.
Any device has the possibility of abnormal function, and the same is true for safety relays. It will also fail due to the abnormal function of a component.
Due to the special logical structure design of the intrinsically safe relay, in the event of any single-function fault, the safety output of the safety relay cannot be caused to malfunction, that is to say, the single fault of the safety relay will not cause the safety output to be in a closed state.
1. Input monitoring of safety conditions: when both channels are closed, the safety relay will be activated, and the safety output will be closed; if one channel is disconnected, the safety output of the safety relay will be disconnected.
2. Start monitoring, the safety relay does not start, of course, the safety output is disconnected. There are two starting conditions:
One is the startup mode: manual startup, automatic startup.
The second is whether the feedback loop is closed. If it is closed, it means that the AC contactor monitored by the safety output of the safety relay did not have a main contact sticking accident in the last breaking, and the function is normal, so that this startup can work normally, the safety relay is activated, and the safety output is closed.
On the contrary, if the feedback loop is disconnected, it means that the AC contactor monitored by the safety output of the safety relay has a main contact sticking accident during the last disconnection, the function is abnormal, the safety relay cannot be started, and the safety output is in a disconnected state.
3. Based on the special structure of the safety relay, the forced-guided relay that constitutes the safety relay, or any device in the logic circuit fails, the safety relay will not start, and its safety output contacts remain disconnected.
To sum up, the role of the safety relay is to ensure the reliable realization of the safety function designed by the safety circuit.